1. Field of the Invention
The present invention generally relates to land structures, printed wiring boards, and electronic devices, and more particularly, to a land structure, printed wiring board, and electronic device wherein an electronic part is soldered.
2. Description of the Related Art
Generally, a land part where a lead of an IC, for example, is soldered has a rectangular configuration. Furthermore, a reflow soldering method or a soldering flow method is used as a method for soldering the lead of the IC, for example, and the land part.
In the reflow soldering method, solder paste or the like is printed in advance on the lead or the land part. After an electronic part is mounted, heat is applied so that the lead and the land part are soldered. Hence, both the printed wiring board and the electronic part are heated.
In this case, according to the reflow soldering method, the amount of the solder can be adjusted in advance so as to be proper. Therefore, even if a pitch between the adjacent leads and lands is set to be narrow, it is possible to prevent a bridge from being generated between the lead and an adjacent land part.
However, since it is required to heat the printed wiring board, it is necessary to use a printed wiring board having a high heating resistance. This increases manufacturing cost. In addition, since it is necessary to apply the solder paste, the number of manufacturing processes is increased.
On the other hand, in the soldering flow, the lead and the land part are soldered by making a printed wiring board where an electric part is tentatively fixed come in contact with a molten solder flow. In the soldering flow, it is not necessary to heat the printed wiring board. Therefore, the heating resistance of the printed wiring board may be low so that the manufacturing cost can be reduced.
However, depending on the direction of flow of the solder, the amount of the supplied solder may be varied in positions of the lead and the land part. Therefore, a bridge is generated between the lead and an adjacent land part in a position where the supplied amount of the solder is large in a case where the pitch between the leads and the lands is narrow. The amount of the solder is insufficient in a position where the supplied amount of the solder is small in a case where the pitch between the leads and the lands is narrow. This causes a bad connection between the lead and the land part.
Because of this, conventionally, the soldering flow cannot correspond to the IC where the pitch between the leads and the lands is narrow.
A soldering terminal having a structure where on a plate surface facing a stretching part of a flat part, a penetrating hole is formed, and a gap is linked with a solder surface of the flat part by the penetrating hole, and fused solder permeates into the gap between the flat part and a pad and a gap between a bent part and the pad, has been suggested. See Japan Laid-Open Patent Application Publication No. 9-223769.
It has been desired that the soldering for the IC where the pitch between the lead and the land is narrow is done by the soldering flow so that the soldering is done easily and at a low cost.